Production of activated char using a moving grate stoker furnace

ABSTRACT

Carbonaceous material is deposited so as to form a bed on a grate moving horizontally through a hot furnace, the furnace having a zoned airbox beneath the grate. Hot combustion byproduct gases are downdrafted through the bed as it passes over airbox zones which are disposed towards the entrance end of the furnace so as to dry and ignite the material and sweep off volatiles therefrom. Air and steam and next air alone and finally steam is fed upwardly through the bed as it progresses beyond the downdrafted zones. Over the bed at the end of the grate run, the downdrafted gases are injected back into the furnace above the bed and burned, and finally the then charred material is quenched by a water spray.

United States Patent [1 1 Whitten et a1.

[ PRODUCTION OF ACTIVATED CHAR USING A MOVING GRATE STOKER FURNACE [76] Inventors: Charles M. Whitten, Rt. 7, Golf Course Ln., Columbia, Tenn. 38401; Robert G. Hagstrom, 2401 Sterling Rd., Nashville, Tenn. 37215 [22] Filed: Aug. 13, 1973 [21] App]. No.: 387,753

Related U.S. Application Data [63] (ontinuation-in-part 01' Ser. No. 130,737. April 12, 1971, abandoned, and a continuation-in-part of Ser. No, 35,771, April 13, 1973, Pat. No. 3,642,170.

[52] U.S. Cl 252/421, 252/445, 201/32,

[51] Int. Cl C10b 49/06 [58] Field of Search 201/17, 32, 36, 38, 37, 201/44; 202/117, 135; 252/421, 445

[56] References Cited UNITED STATES PATENTS 3,146,175 8/1964 Mansfield 201/32 X 1 Mar. 11, 1975 3,167,487 l/l965 Mansfield ..20 l/32X 3,434,933

3/1969 Mansfield 201/32 Primary Examiner-Wilbur L. Bascomb, Jr. Assistant ExaminerDavid Edwards [57] ABSTRACT Carbonaceous material is deposited so as to form a bed on a grate moving horizontally through a hot furnace, the furnace having a zoned airbox beneath the grate. Hot combustion by-product gases are downdrafted through the bed as it passes over airbox zones which are disposed towards the entrance end of the furnace so as to dry and ignite the material and sweep off volatiles therefrom. Air and steam and next air alone and finally steam is fed upwardly through the bed as it progresses beyond the downdrafted zones. Over the bed at the end of the grate run, the downdrafted gases are injected back into the furnace above the bed and burned, and finally the then charred material is quenched by a water spray.

5 Claims, 2 Drawing Figures PRODUCTION OF ACTIVATED CHAR USING A MOVING GRATE STOKER FURNACE RELATED APPLICATIONS Whitten and Hagstrom, PRODUCTION OF ACTI- VATED CHAR USING A MOVING GRATE STO- KER FURNACE, Ser. No. 130,737 filed Apr. 12, 1971, and now abandoned of which this is a continuation-inpart; and Hagstrom, WATER SPRAY OVER TRANS- FER MECHANISM FOR COOLING CI-IARS, Ser. No. 35,771 filed Apr. 13, 1973, and now US. Pat. No. 3,642,170.

FIELD OF INVENTION Compositions, Processes, including carbonization, and Free carbon containing, and Processes including oxidation or gas treatment: Distillation: Processes, Thermolytic, Including Burning of Vaporized Product.

PRIOR ART US. Pat. Nos. Sauer 1,502,592; Barnaby et a1 1,541,099; Mansfield 3,434,932; and Mansfield 3,434,933.

OBJECTS Heretofore, methods for producing activated char have been devised, but, so far as is known, the production of activated char in a chain grate stoker furnace has never been achieved by others. This type of furnace, used in the Mansfield coking processes (supra), lends itself to the achievement of several unique advan-. rages, some being that excessive burning of the fixed carbon can be avoided by using only the bare minimum of air required for oxidation, spurious coking of the carbonaceous material is avoided by accurate heat control at the points where spurious coking might otherwise occur, desirable particle size of the char granules can be maintained because of the static-bed nature of the process, removal of comparative large amounts of water from the starting material can be accomplished by the same feature of the process (downdrafting at the front of the furnace, and feeding of the downdrafted gases to the rear of the furnace) by which a reducing atmosphere above the bed is maintained.

While certain superficial similarities to the Mansfield coking processes prevail, the process of producing activated char is far different from coking processes. For one thing, while many carbonaceous materials, namely wood, peat, brown coal, lignite, sub-bituminous, bituminous, semi-antrhacitic, and anthracite coals may be used, the starting materials for char are generally the lower ranked coals, peat and lignite, because of their inexpensiveness and availability. Also, in the production of activated char, coking of the material is to be avoided. Unlike coking processes, the production of activated char entails the reaction, in a reducing atmosphere, of steam on carbon which has been heated, for example, to about l,580 F in the presence of minimal air, CO and CO and, in the subject case, the prompt quenching of the char once it has been produced.

These and other objects will be apparent from the following specification and claims, in which:

FIG. 1 is a diagrammatic longitudinal cross-section illustrating the char-producing process; and,

FIG. 2 is a diagrammatic transverse cross-section illustrating the quenching process.

Referring now to the drawing, in which like reference numerals denote similar elements, FIGS. 1 and 2 diagrammatically illustrate the apparatus in which the subject process is carried out. The starting material is fed from a storage receptacle 10 through a scale 12 to a hopper 14 at the input end of a carbonizing furnace 16. As previously stated, the starting material may be anyone or more of various carbonaceous materials. Petroleum coke would not be used because too much of its carbon would have to be burned in the process. Since lignite is readily available and has been proven to be satisfactory in this process, the process will be described wherein lignite is the starting material, namely, Velva Seam lignite obtained from near Minot, North Dakota. The lignite was sized 1% inches X 1% inch, with the following typical analysis:

The lignite is spread on a chain grate 18 by a spreader gate 20 to form a bed 22. The chain grate is driven by conventional sprockets 23,24 which rotate as denoted by the curved arrows so that the bed moves from the front end 25 to the rear end 26 of the furnace, and in so doing, it passes over the zones 1-6 of a zoned airbox 27. The lignite, in passing through the furnace, is converted to activated char. Upon reaching the rear end 26 of the furnace, the then hot char drops into a trough 28 from which it is fed sidewise by a screw 30. While in trough 30 the char is quenched by water from sprays 32. From trough 30 the then partly quenched char is fed through an open end of the trough into a tank 36, where it is further quenched by water from sprays 35 as it drops onto the top of the stack 37 in the tank. The sidewise feed and quenching mechanism is the subject of the Hagstrom application (supra). Quenched char from bottom of the stack is discharged via an air lock gate 38 into a tumbler 40, where the surface ash is knocked off, and the char is shattered so that it assumes a size of about 6 X 30 mesh. Any coke or nondevolatilized char will not shatter, and hence it is taken off by the next stage, i.e., a screen 42 in which the output material is separated into coke, activated char, and ash. The proximate analysis of the char product is as follows:

As Received Dry Basis Moisture 1.62

% Ash 13.74 13.97

% Volatile 11.16 11.34

% Fixed Carbon 73.48 74.69 Btu 11,671 11,863

% Sulfur 0.28 0.28

tion. The invention is concerned with the processing of the material as it passes from the front end 25 to the rear end 26 of the furnace. At start-up, the furnace is preheated by building a tire on the grate. Airbox zone 1 is not used in the following example, since it was found that the desired bulk treatment could be attained by utilizing the airbox zones 2-6.

The incoming lignite is first completely dried and greatly de-volatilized as it passes over airbox zones 2 and 3, into which hot gases at about l,2 O from above the bed are downdrafted. In passing through the lignite which is then passing over. zones 2 and 3, the downdrafted gases give up heat to the lignite so that the gas temperature drops to about 400 F to 500 F, at which temperature these gases can be handled by a fan 44, al-

' though they are too hot to condense. As diagrammed in FIG. 1, fan 44 draws the gases through downdraft lines 46, 48 which are controlled by valves 50 and 52 so that the desired ratio of downdrafting through airbox zones 2 and 3 can be maintained. From fan 44 the downdrafted gases, then consisting largely of moisture and volatiles, and being devoid of oxygen, are fed to a jet 56 disposed over the bed at the rear end of the furnace, so as to create a reducing atmosphere above the bed.

As the lignite progresses over airbox zones 4 and 6, steam is fed upwardly through the bed from a steam line 58 and through branches 60 and 62 controlled by valves 64 and 66. The main purpose of feeding steam through the bed via airbox zone 4 is to control the amount of burning produced by the air feed through airbox zone 4 described below. The purpose in feeding steam through the bed via airbox zone 6 is to greatly reduce the temperature of the hot lignite from about l',5 80 F to about 780 F and, in the reducing atmosphere previously described, to produce the reaction which produces the activated char.

As the bed progresses over airbox zones 4 and 5, air

I (in addition to the steam fed via airbox zone 4) is forced upwardly through the lignite by a fan 68 and branch lines 70 and 72 controlled by valves 74 and 76. Sufficient air is fed to the bed to raise it to about l,380 at the end of airbox zone 4 and thence to about 1,580

through these that air (and termpering steam) is fed up- .wa'rdly through the bed; and'the third airbox zone F at the end of airbox zone 5. The gaseous by-products downdrafted, and they are the first active zones; the

second airbox zones means shall be taken to means zones 4 and 5, since they function similarly and itis means shall be taken to mean airbox zone 6, since it is through this one that steam is fed upwardly through the bed. These terms are intended to cover other arrangements and numbers of airbox zones which function similarly.

Iclairn:

1. The method of making activated carbon from a carbonaceous starting materialselected from the class consisting of wood, p'eat, brown coal, lignite, subbituminous coal, bituminous coal, semi-anthracite coal and antracite coal, which method-comprises,

continuously depositing said starting material onto a continuously moving grate running horizontally from front to rear through a hot carbonizing furnace and, in so doing, passes over a series of first, second and third airbox zone means consecutively arranged from front to rear of the furnace, downdrafting hot gases through the bed from above that portion of the bed which is disposed towards the rear of the furnace from the first airbox zone means as the bed moves over first airbox zone means so as to drive off moisture and volatile mat; ter from and pre-heat the material, simultaneously feeding air upwardly through the bed as the latter passes over the second airbox zone means and thereby raising the bed temperature from the pre-heat temperature to a charring temperature, simultaneously feeding steam upwardly through the bed as the latter passes over third airbox zone means so as to reduce the bed temperature, and simultaneously feeding the downdrafted gases ladened with moisture and volatile matter into the rear portion of the furnace over that portion of the bed which is then passing over the third airbox zone means and thereby maintaining a reducing atmosphere in the furnace over the bed.

2. The method recited in claim 1, wherein the bed temperature, in passing over the second airbox zone means, is raised to about 1580 F.

3. The method recited in claim 2, including the step of feeding steam upwardly through the bed while the latter passes over at least part of the second airbox zone means so as to reduce the amount of combustion produced in the bed by the air fed therethrough.

rial passes over said third airbox zone means. 

1. The method of making activated carbon from a carbonaceous starting material selected from the class consisting of wood, peat, brown coal, lignite, subbituminous coal, bituminous coal, semi-anthracite coal and antracite coal, which method comprises, continuously depositing said starting material onto a continuously moving grate running horizontally from front to rear through a hot carbonizing furnace and, in so doing, passes over a series of first, second and third airbox zone means consecutively arranged from front to rear of the furnace, downdrafting hot gases through the bed from above that portion of the bed which is disposed towards the rear of the furnace from the first airbox zone means as the bed moves over first airbox zone means so as to drive off moistuure and volatile matter from and pre-heat the material, simultaneously feeding air upwardly through the bed as the latter passes over the second airbox zone means and thereby raising the bed temperature from the pre-heat temperature to a charring temperature, simultaneously feeding steam upwardly through the bed as the latter passes over third airbox zone means so as to reduce the bed temperature, and simultaneously feeding the downdrafted gases ladened with moisture and volatile matter into the rear portion of the furnace over that portion of the bed which is then passing over the third airbox zone means and thereby maintaining a reducing atmosphere in the furnace over the bed.
 1. THE METHOD OF MAKING ACTIVATED CARBON FROM A CARBONACEOUS STARTING MATERIAL SELECTED FROM THE CLASS CONSISTING OF WOOD, PEAT, BROWN COAL LIGNITE, SUBBITUMINOUS COAL, BITUMINOUS COAL, SEMI-ANTHRACITE COAL AND ANTRACITE COAL, WHICH METHOD COMPRISES, CONTINUOUSLY DEPOSITING SAID STARTING MATERIAL ONTO A CONTINUOUSLY MOVING GRATE RUNNING HORIZONTALLY FROM FRONT TO REAR THROUGH A HOT CARBONIZING FURNACE AND, IN SO DOING, PASSES OVER A SERIES OF FIRST, SECOND AND THIRD AIRBOX ZONE MEANS CONSECUTIVELY ARRANGED FROM FRONT TO REAR OF THE FURNACE, DOWNDRAFTING HOT GASES THROUGH THE BED FROM ABOVE THAT PORTION OF THE BED WHICH DISPOSED TOWARDS THE REAR OF THE FURNACE FROM THE AIRBOX ZONE MEANS AS THE BED MOVES OVER FIRST AIRBOX ZONE MEANS SO AS TO DRIVE OFF MOISTURE AND VOLATILE MATTER FROM AND PRE-HEAT THE MATERIAL, SIMULTANEOUSLY FEEDING AIR UPWARDLY THROUGH THE BED AS THE LATTER PASSES OVER THE SECOND AIRBOX ZONE MEANS AND THEREBY RAISING THE BED TEMPERATURE FROM THE PRE-HEAT TEMPERATURE TO A CHARRING TEMPERATURE, SIMULTANEOUSLY FEEDING STEAM UPWARDLY THROUGH THE BED AS THE LATTER PASSES OVER THIRD AIRBOX ZONE MEANS SO AS TO REDUCE THE BED TEMPERATURE, AND
 2. The method recited in claim 1, wherein the bed temperature, in passing over the second airbox zone means, is raised to about 1580* F.
 3. The method recited in claim 2, including the step of feeding steam upwardly through the bed while the latter passes over at least part of the second airbox zone means so as to reduce the amount of combustion produced in the bed by the air fed therethrough.
 4. The method recited in claim 3, wherein the bed is quenched to about 780* while passing over the third airbox zone means. 